There is known from CH Patent No 705238 a balance with clamped inertia blocks for adjusting the inertia and/or poise of the balance. The balance has two arms each including a housing for receiving and clamping in position an arbor of an inertia block, the head of the inertia block resting against the front face of the balance.
The balance described above has several drawbacks. It will be mentioned first of all that access to the inertia blocks may be difficult depending on the architecture of the movement and may make the inertia adjustment complicated, which may result in increased adjustment costs. Moreover, such a balance takes up a relatively large amount of place, since the head of the inertia blocks rests in the balance recess, which may result in an increase in the thickness of the movement.
There is also known from EP Patent No 1351103 a balance with inertia adjustment for a timepiece movement wherein the rim has recessed portions for receiving inertia blocks so that there are no protruding parts. Although this facilitates the adjustment of the balance, machining is required to form the recessed portions, which is relatively difficult, time-consuming and expensive.